Power transmitting method and power transmitter for communication with power receiver

ABSTRACT

A method and power transmitter for efficiently controlling power transmission to one or more power receivers in a wireless multi-power transmission system are provided. The method includes performing, when a predetermined measurement cycle arrives, a load measurement; comparing a current load measurement value with a previous load measurement value; determining whether the current load measurement value is increased over the previous load measurement value by at least as much as a first predetermined threshold; gradually increasing, when the load measurement value is increased over the previous load measurement value by at least as much as the first threshold, a transmission power value until a request for a subscription to a wireless multi-power transmission network from a power reception target within a predetermined time limit; and stopping, when the request for the subscription is not received before the time limit is exceeded, power transmission to the power reception target.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to anapplication filed in the Korean Industrial Property Office on May 17,2011 and assigned Serial No. 10-2011-0046395, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a wireless power transmissionsystem, and more particularly, to a power transmitting method forcommunication with a power receiver in a wireless multi-powertransmission system.

2. Description of the Related Art

A wireless power transmission system typically includes a powertransmitter and a power receiver. Power transmission between the powertransmitter and the power receiver is configured such that power istransferred between a first coil of the power transmitter and a secondcoil of the power receiver. Such a configuration is commonly used invarious power transmission systems.

A communication technique used in the wireless power transmission systemhaving the above configuration may be divided into two schemes. One suchscheme is an In-Band communication scheme that performs communicationthrough a coil that transfers power, and the other such scheme is anOut-Band communication scheme that performs communication through acommunication end that is separate from the coil that is transferringpower.

The wireless power transmission system employing such wireless chargingtechnologies includes a power transmitter in a form of a power supplyingsupporter, and is configured such that the power transmitter suppliespower to the power receiver such as a mobile terminal. A wireless powertransmission system can also be configured such that wireless chargingbetween power receivers is possible by sharing a battery installed inthe power receiver even without the power supplying supporter. Asdescribed above, when the wireless charging between the power receiversis possible, the power receivers can be operated without powertransferred from the power transmitter. However, most power receiversare operated by power received from the power transmitter such as thepower supplying supporter.

However, when the power receiver is operated by power supplied from thepower transmitter while performing communication according to theOut-Band communication scheme, if sufficient power is not supplied fromthe power transmitter, the power receiver may not operate normally. Forexample, when the power receiver is not fully located within aneffective area where the power receiver can receive power transferredfrom a nearby power transmitter, or when a plurality of power receiversare located in the effective area so as to share power for communicationfrom the power transmitter at the same time, it may not be possible forall power receivers to obtain equal charging efficiency and powertransmission efficiency is also deteriorated. Accordingly, some of orall of the power receivers may not receive sufficient power.

Accordingly, a power receiver that does not normally receive sufficientpower may not be able to perform communication. When the powertransmitted is not sufficient to perform communication with the powerreceiver, the power transmitter does not supply power to the powerreceiver and may not recognize the power receiver as a valid receiver.

SUMMARY OF THE INVENTION

The present invention has been made to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. In, in order to address the problem occurring due toinsufficient power supplied to the power receiver, an aspect of thepresent invention is to provide a power transmitting method and a powertransmitter for efficiently supplying power to a power receiver.

According to another aspect of the present invention provides, a powerreceiving method and a power transmitter are provided for efficientlycontrolling power transmission to each of a plurality of powerreceivers, when the plurality of power receivers is located in aneffective charging area.

In accordance with an aspect of the present invention, a method ofcontrolling power transmission for communication with one or more powerreceivers by a power transmitter is provided. The method includesperforming, when a predetermined measurement cycle arrives, a loadmeasurement; comparing a current load measurement value corresponding tothe load measurement with a previous load measurement value; determiningwhether the current load measurement value is increased over theprevious load measurement value by at least as much as a firstpredetermined threshold; gradually increasing, when the load measurementvalue is increased over the previous load measurement value by at leastas much as the first threshold, a transmission power value until arequest for a subscription to a wireless multi-power transmissionnetwork from a power reception target within a predetermined time limit;and stopping, when the request for the subscription is not receivedbefore the time limit is exceeded, power transmission to the powerreception target.

In accordance with another aspect of the present invention, a powertransmitter for controlling power transmission for communication withone or more power receivers is provided. The power transmitter includesa communication unit for performing wireless communication; a powersupplier for supplying a power source to generate a resonance frequencysignal determined by a controller; a voltage/current measurement unitfor measuring a voltage and a current of the generated resonancefrequency signal; a resonance signal generator for transmitting powertransferred from the power supplier to at least one power receiver; andthe controller for controlling transmission of power for communicationthrough the resonance signal generator when the voltage/currentmeasurement unit detects a load change at least equal to a predeterminedthreshold, gradually increasing a transmission power value until arequest for a subscription to a wireless multi-power transmissionnetwork is received within a predetermined time limit, and stoppingtransmission of the power to a power reception target when the requestfor the subscription is not received before the time limit is exceeded.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is diagram illustrating a configuration of a wireless multi-powertransmission system according to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating a power transmitter and a powerreceiver in a wireless multi-power transmission system according to anembodiment of the present invention;

FIG. 3A is a diagram illustrating an operation for periodic loaddetection of a power transmitter when there is no power receiverreceiving power from the power transmitter;

FIG. 3B is a diagram illustrating an operation for periodic loaddetection of a power transmitter when there is a power receiverreceiving power from the power transmitter;

FIG. 4 is a flowchart illustrating an operation for periodic loaddetection by a power transmitter;

FIG. 5 is a flowchart illustrating an operation for a process ofchanging a power transmission value after a load detection by a powertransmitter according to an embodiment of the present invention;

FIGS. 6A and 6B are diagrams illustrating an operation of changing apower transmission value when a target of power reception is detected ina state where there is no power receiver according to an embodiment ofthe present invention; and

FIGS. 7A and 7B are diagrams illustrating an operation of changing apower transmission value when a target of power reception isadditionally detected in a state where there is a power receiveraccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Hereinafter, embodiments of the present invention are described withreference to the accompanying drawings. In the following description andthe accompanying drawings, a detailed description of known functions andconfigurations incorporated herein may be omitted to avoid obscuring thesubject matter of the present invention.

According to an embodiment of the present invention, a method ofefficiently controlling power transmission to one or more powerreceivers in the wireless multi-power transmission system is provided.To this end, the method includes performing a load measurement when apredetermined measurement cycle arrives, comparing a load measurementvalue according to the load measurement with a previous load value;determining whether the load measurement value is increased by a firstthreshold or more from the previous load value, when the loadmeasurement value is increased by the first threshold or more from theprevious load value, gradually increasing a transmission power valueuntil a request for a subscription to a wireless multi-powertransmission network from a target of power reception within apredetermined time limit, and, when the request for the subscription isnot received until the time limit is exceeded, stopping the powertransmission to the target of power reception.

Herein, invalid material is defined as a material that receives, when apower transmitter transmits power, power intended for other powerreceivers. Examples of invalid material may include a metal material, anelectronic device that does not perform communication with the powertransmitter, and a power receiver to which the power transmitter doesnot intend to transmit the power. In the following description, such aninvalid material may also be referred to as a non-target of powerreception.

Hereinafter, a configuration of a wireless power transmission systemaccording to an embodiment of the present invention is described withreference to FIG. 1.

Referring to FIG. 1, a power transmitter 30 detects that the presence ofa target to receive power on a charging deck by using a load detectionfunction, and can transmit wireless power to one or more powerreceivers. The power transmitter 30 and a power receiver 31 performcommunication with each other through a communication system separatefrom the wireless power transmission system.

When the power receiver 31 is located within an effective range of afirst coil of the power transmitter 30, that is, in an effectivecharging area, a value of a voltage (or current) measured in the firstcoil of the power transmitter 30 is changed. That is, a measured voltagevalue is changed by a change in a load. However, when an invalid powerreceiver 32 or an invalid material 33 is located within the effectiverange of the first coil of the power transmitter 30, the same phenomenonmay be also generated.

The components in FIG. 1 according to embodiments of the presentinvention are described in detail herein with reference to FIG. 2.

Due to power transmission to a non-target of intended power reception,the efficiency of the power transmission is deteriorated and a breakdownby an overload or an accident by overheating may be generated.Accordingly, in order to guarantee the safety of the wireless powertransmission system it is necessary to stop the power transmission tothe non-target of the intended power reception.

As described above, an embodiment of the present invention provides awireless power transmission system including the power transmitterhaving a function of transmitting wireless power to a plurality of powerreceivers and power receivers having a function of receiving wirelesspower. According to such an embodiment of the present invention, eventhough one or more targets of charging are located in the effectivecharging area, power can be transmitted to only an effective target ofpower reception among the multiple targets of charging.

A power transmission method for communication with one or more targetsof power reception according to an embodiment of the present inventionis described as follows with reference to FIG. 2.

FIG. 2 is a block diagram illustrating insides of a power transmitterand a power receiver included in a wireless power transmission system ofFIG. 1 according to an embodiment of the present invention.

Referring to FIG. 2, a power transmitter 100 includes a power supplier10, an amplifier 12, a resonance signal generator 14, a voltage/currentmeasurement unit 16, a controller 18, and a wireless communication unit19. The power supplier 10 supplies power in a manner that generates aresonance frequency signal determined by a controller 18. The powersupplier 10 may include a Voltage Control Oscillator (VOC), for example.The amplifier 12 amplifies the signal generated by the power supplier 10to a signal of a high output according to power applied from the powersupplier 10. The resonance signal generator 14 transmits power from thepower supplier 10 to one or more power receivers through a wirelessresonance signal according to the signal of the high output generated bythe amplifier 12. The voltage/current measurement unit 16 measures avoltage and a current generated by the power supplier 10. The controller18 generally controls a wireless power transmission operation of thepower transmitter 100, and in particular, controls operations of thepower supplier 10 and the amplifier 12 to maintain a preset value withina normal range by monitoring a voltage and a current of a resonancesignal wirelessly transmitted according to the current and the voltagedetected by the voltage/current measurement unit 16. The wirelesscommunication unit 19 is configured by applying one selected schemeamong various wireless short-distance communication schemes such asBluetooth, for example, for communication with a power receiver 110 inconnection with the wireless power transmission operation under acontrol of the controller 18. Here, the resonance signal generator 14includes a charging substrate that can place the power receiver abovethe resonance signal generator 14.

After detecting a change in a load and when the load measurement valueis increased over the previous load measurement value by at least asmuch as the first threshold, the controller 18 controls a gradualincrease of a transmission power value until a request for asubscription to a wireless multi-power transmission network from a powerreception target within a predetermined time limit, and stopstransmission of the power to a power reception target when the requestfor the subscription is not received before the time limit is exceeded.

The controller 18 of the power transmitter 100 may include a MicroController Unit (MCU) and/or other similar components (not shown). Anoperation for controlling power transmission to one or more powerreceivers according to the present invention is described in detailherein with reference to FIGS. 4 and 5.

Meanwhile, the power receiver 110 includes a resonance signal receiver24, a rectifier 22, a regulator 21, a constant voltage generator 20, avoltage measurement unit 26, a controller 28, and a wirelesscommunication unit 29. The resonance signal receiver 24 receives thewireless resonance signal transmitted from the resonance signalgenerator 14. The rectifier 22 rectifies an Alternating Current(AC)-type power source received by the resonance signal receiver 24 to aDirect Current (DC)-type power source. The regulator 21 regulates the DCpower source rectified by the rectifier 22. The constant voltagegenerator 20 converts a power source output from the regulator 21 to anoperation power source (e.g. +5 V) desired by a portable terminal andthe like to which a corresponding power receiver is applied. The voltagemeasurement unit 26 measures an input voltage. The controller 28 forgenerally controls a wireless power reception operation of the powerreceiver 110, determines a power reception state according to a detectedsignal of a constant voltage detector 26, and provides information onthe power reception state. The controller 28 of the power receiver alsomay include an MCU and/or other similar components.

The wireless communication unit 29 is configured by applying oneselected scheme among various wireless short-distance communicationschemes for communication with the power transmitter 100 in connectionwith the wireless power reception operation under a control of thecontroller 28. The wireless communication unit 29 can transmit andreceive various types of information pieces and messages required in awireless charging process through wireless short-distance communicationunder the control of the controller 28.

The aforementioned power transmitter 100 performs a load measurementbased on a predetermined measurement cycle (T_cycle) as shown in FIG.3A. Such a measurement cycle corresponds to a time interval fordetecting a change in a load by the power transmitter 100. FIG. 3Aillustrates an example of a load measurement when there is no powerreceiver in an effective charging area of the power transmitter 100. Asshown in FIG. 3A, the power transmitter 100 transmits power having apredetermined size in order to detect whether there is a change in aload based on a predetermined measurement cycle. Power corresponding tothis load detection is referred to as “P_detection”.

As explained above, FIG. 3A illustrates an example where there is nopower receiver for receiving power from the power transmitter 100.Accordingly, the power transmitter 100 does not transmit power before anext measurement cycle after transmitting the load detection power forthe load measurement.

FIG. 3B illustrates an example of a load measurement where the powertransmitter 100 is transmitting power to the power receiver 110 locatedin the effective charging area. An amount of power being currentlytransmitted to the power receiver 110 is referred to as “P_present”. Thepower transmitter 100 performs a load measurement based on apredetermined measurement cycle, even while transmitting the size ofcurrent transmission power (P_present) to the power receiver 110. Indetail, the current transmission power (P_present) refers to powertransmitted by the power transmitter 100 for the power receiver 110 thatis already receiving power. The load detection power (P_detection) maybe less than the current transmission power (P_present) for chargingsince the load detection power (P_detection) is a minimum power used todetermine whether the power receiver is present.

A process of the load measurement is described in detail as follows withreference to FIG. 4. FIG. 4 is a flowchart illustrating an operation forperiodical load detection by a power transmitter

Referring to FIG. 4, in step, 400, the power transmitter 100 determineswhether a load value has been previously stored through a previousmeasurement. Herein, a previous load value refers to a load value thatis set in a previous step and maintained by the power transmitter 100.If there is no previous load value, an initial load value is set to theprevious load value in step 405. Herein, a parameter indicating theprevious load value is referred to as “D_before” and a parameterindicating the initial load value is referred to as “D_Init”, andD_before” is substituted with “D_Init”. Herein, the initial load value(D_Init) is a load value measured while the power transmitter 100transmits power having a same size as the current transmission power(P_present) through a first coil when there is no object adjacent to thepower transmitter 100. The initial load value (D_Init) is a valuemeasured by converting a sine wave of the first coil to a DC-type sinewave, and the initial load value (D_Init) may be a peak value of avoltage applied to the first coil or may include electrical propertiesthat can be measured through the first coil among frequencies of thefirst coil.

Subsequently, the power transmitter 100 stores a current time at whichthe load is measured in step 410. The load is measured by converting asine wave applied to the first coil to a sine wave corresponding todirect current, and accordingly a load measurement value is obtained.Here, a parameter indicating the load measurement value is referred toas “D_measure”, and a parameter indicating the current time is referredto as “T_det_now”.

The power transmitter 100 compares the previous load value (D_before)and the load measurement value (D_measure) in step 415. Through a resultof the comparison, the power transmitter 100 determines whether there isa change in the load, in step 410. Specifically, the power transmitter100 determines whether a difference between the load value (D_before)and the load measurement value (D_measure) is within a margin of errorby considering a communication environment between the load value(D_before) and the load measurement value (D_measure). If the load value(D_before) and the load measurement value (D_measure) are the same(i.e., if the difference between the two values is within the margin oferror), the power transmitter 100 proceeds to step 419 and thusdetermines that no target of power reception has newly entered andmaintains a transmission power value. For example, when a power receiverthat is already being charged is present in the effective charging areaas shown in FIG. 3B, a current transmission power value is maintained.When there is no power receiver in the effective charging area, atransmission power value corresponding to “0” is maintained as shown inFIG. 3A. Further, when the power transmitter 100 determines that thereis no target of power reception that newly or additionally enters theeffective charging area, the power transmitter 100 proceeds to step 445.

Meanwhile, if the power transmitter 100 determines that there is thechange in the load in step 417, the power transmitter 100 determineswhether the load measurement value is increased by at least firstthreshold from the previous load value in step 420. If the loadmeasurement value is increased by at least the first threshold from theprevious load value, the power transmitter 100 proceeds to step 425, anddetermines that the target of power reception is located in theeffective charging area. More specifically, the power transmitter 100determines that a load change higher than the first threshold isgenerated due to the target of power reception. Accordingly, the powertransmitter 100 changes the transmission power value for powertransmission to the power receiver in step 435.

If the load measurement value is not increased by at least the firstthreshold from the previous load value in step 420, the powertransmitter 100 determines whether the load measurement value isdecreased by at least a second threshold from the previous load value instep 430. If the load measurement value is decreased by at least thesecond threshold from the previous load value, the power transmitter 100proceeds to step 440, and determines that the target of power receptionhas disappeared. Then, the power transmitter 100 changes thetransmission power value in step 435. More specifically, the powertransmitter 100 stops transmitting power to the target of powerreception.

Thereafter, the power transmitter 100 stores the load measurement valueas the previous load value in step 445. Accordingly, D_before=D_measure.A passed current time (i.e., new current time for determining time thathas passed since the current time was previously measured and stored instep 410) is stored in step 450. Here, a parameter indicating the passedcurrent time is defined as “T-det after”. Further, the power transmitter100 determines whether a measurement cycle is passed in step 455.Whether the measurement cycle is passed is determined using an equationof “T_det_now+T_cycle≦T_det_after”.

If it is determined that the measurement cycle is not passed in step455, the power transmitter 100 returns to step 450 and stores a currenttime passed from the current time stored in step 410 in order todetermine whether the measurement cycle is passed. If it is determinedthat the measurement cycle is passed in step 455, the power transmitter100 returns to step 410 and performs the load measurement according to anext measurement cycle. As described above, the load measurement isperformed during each measurement cycle by repeating steps 410 to 455.

Hereinafter, a process of changing the power transmission value in thepower transmitter 100 is described as follows with reference to FIG. 5.FIG. 5 is a flowchart illustrating an operation for a process ofchanging a power transmission value after a load detection by a powertransmitter according to an embodiment of the present invention.

FIG. 5 corresponds to an operation process performed after adetermination that there is the target of power reception when the loadmeasurement value is increased by at least the first threshold. Forbetter understanding, the following description according to anembodiment of the present invention also refers to FIGS. 6A and 6B.FIGS. 6A and 6B are diagrams illustrating an operation of changing apower transmission value when a target of power reception is detected ina state where there is no power receiver according to an embodiment ofthe present invention.

First, the power transmitter 100 transmits power having a size of loaddetection power (P_present) to detect a load and performs a loadmeasurement 600 as shown in FIG. 6A. Here, a detection of the loadchange is implemented through the same process as that described withreference to FIG. 4.

Accordingly, if the load change is detected in step 500, the powertransmitter 100 transmits power for communication in step 505. Upon adetermination that a target of charging which can receive power at atime point of A within the measurement cycle (T_cycle) is located in theeffective charging area after the load measurement, the powertransmitter 100 performs power transmission for communication with thetarget of charging. Accordingly, the power transmitter 100 transmitspower having a size of first communication power (P_communication_1), asshown in FIG. 6A. Here, the first communication power(P_communication_1) refers to a quantified power value with which thecontroller 28 and the wireless communication unit 29 within the powerreceiver can be operated.

The power receiver, which is the target of charging that has receivedpower, transmits a network subscription request message for asubscription to a network. Here, wireless multi-power transmission isachieved, and the network is defined as a configuration including atleast one power receiver and the power transmitter for transmittingpower to the plurality of power receivers.

In step 510, the power transmitter 100 determines whether the networksubscription request message is received from the target of chargingwithin a predetermined time. Here, the predetermined time corresponds to“T_c” in FIG. 6A, and refers to a time during which the powertransmitter 100 waits for the network subscription request message whiletransmitting predetermined power, i.e., the first communication power(P_communication_1) for communication with the target of charging.

If the network subscription request message is not received within thepredetermined time, the power transmitter 100 determines whether a timelimit is exceeded in step 515. Here, the time limit corresponds to“T_joinlimit” in FIG. 6A. If it is determined that the time limit is notexceeded in step 515, step 525 is performed and the power transmissionvalue is increased. At this time, the network subscription requestmessage is not received within the predetermined time (T_c) that doesnot exceed the time limit (T_joinlimit), because insufficient power issupplied to the target of charging and thus no communication isperformed, so that the transmission power value is increased.Accordingly, the power transmitter 100 increases the currenttransmission power value corresponding to the size of the firstcommunication power (P_communication_1) to a transmission power valuehaving a size of second communication power (P_communication_2) as shownin FIG. 6A. Next, if the network subscription request message is notstill received, even though the increased transmission power value, thepower transmitter 100 further increases the transmission power valuefrom the size of the second communication power (P_communication_2) to atransmission power value having a size of third communication power(P_communition_3). In this process, a difference between the firstcommunication power (P_communication_1) and the second communicationpower (P_communication_2) and a difference between the secondcommunication power (P_communication_2) and the third communicationpower (P_communition_3) are determined through division intopredetermined units within a maximum transmission power value.

Thereafter, if the network subscription request message is not receiveduntil the time limit (T_joinlimit) is exceeded, the power transmitter100 determines the target of charging as the non-target of powerreception in step 520. As shown in FIG. 6A, if the network subscriptionrequest message is not received even though the transmission power valueis increased to the transmission power value in a range of the size ofthe first communication power (P_communication_1) to the size of thethird communication power (P_communition_3), the power transmitter 100determines the target of charging as the non-target of power receptionin a time point at which the time limit (T_joinlimit) is exceeded, thatis, a time point of B.

For example, although the invalid material such as a metal material cangenerate a voltage value or a current value measured in the powertransmitter 100 change, the invalid material cannot respond to powertransmission of the transmitter 100, since the invalid material cannotperform communication. More specifically, the invalid material cannotinform the transmitter that the invalid material is an effective powerreceiver. Accordingly, the invalid material or the ineffective powerreceiver cannot transmit the network subscription request message eventhough the time limit is exceeded. The power transmitter 100 considersthat the communication has not been performed when the networksubscription request message has not been received, so that the powertransmitter 100 determines the target of charging that has generated theload change is a non-target of power reception, i.e., the powertransmitter 100 determines that the load change has been generated bythe invalid material.

However, if the network subscription request message is received withinthe time limit (T_joinlimit) in step 510, the power transmitter 100compares a reference load value and a changed load value obtainedthrough the load detection in step 530. FIG. 6B illustrates an examplewhere the network subscription request message is received at a timepoint of D when the power transmitter transmits a transmission powervalue having a size of the first communication power(P_communication_1), since the power transmitter determines that thereis a target of charging that can receive power at a time point of Cafter the load measurement 610 and then the power transmitter increasesthe transmission power value to a transmission power value having a sizeof the second communication power (P_communication_2).

At this time, the network subscription request message includes initialinformation for informing the transmitter that the power receiver is atarget of charging and an effective power receiver. The initialinformation contains an ID of the power receiver, a protocol version, areference load value in the power receiver, and a reference efficiencyvalue in the power receiver. Accordingly, the power transmitter 100 setsa reference load value by reflecting the reference load value of thepower receiver contained in the network subscription request message inorder to know a load value changed when the power receiver is located inthe effective charging area. For example, if a measurement value whenthere is no power receiver in the effective charging area of the powertransmitter 100 is A and a measurement value changed as the powerreceiver is located in the effective charging area is B, a valuequantified from the changed measurement value, for example, a differencebetween A and B or B is defined as a reference load.

The power transmitter determines whether a result of the comparisonbetween the reference load value and the changed load value is within anacceptable range in step 535. Here, the acceptable range may be a rangebased on a reference change value, and, in this case, it can bedetermined whether the changed load value is within the acceptablerange.

If the result of the comparison exceeds the acceptable range in step535, the power transmitter 100 proceeds to step 520 and the powertransmitter 100 determines that the power receiver having transmittedthe network subscription request message can perform communication butdetermines the power receiver as the non-target of power reception whichis not suitable for performing wireless charging with the powertransmitter 100. For example, the power transmitter 100 determines thepower receiver is a device that cannot perform wireless charging set bya manufacturer or a regulation. Accordingly, the power transmitter 100proceeds to step 550 and stops transmitting power to the target ofcharging.

If the result of the comparison is included within the acceptable rangein step 535, the power transmitter 100 determines the power receiverhaving transmitted the network subscription request message is aneffective power receiver and determines whether the power receiver cansubscribe to the network in step 540. More specifically, the powertransmitter 100 determines whether the power receiver can subscribe tothe network for wireless multi-power transmission. For example, if thepower transmitter 100 determines that a number of power receivers hasalready reached a maximum number of targets of charging, it may bedifficult for additional power receivers having transmitted the networksubscription request message to join the network. Further, when aprotocol version of the power receiver is greater than a protocolversion of the wireless multi-power transmission network, it may bedetermined that the power receiver cannot subscribe to the wirelessmulti-power transmission network.

Accordingly, if the power receiver cannot subscribe to the network instep 540, the power transmitter 100 transmits a network subscriptionrejection message to the power receiver having transmitted the networksubscription request message in step 545. Subsequently, the powertransmitter 100 stops transmitting power to the corresponding target ofcharging, i.e., the power receiver having transmitted the networksubscription request message in step 550. However, if the power receivercan subscribe to the network in step 540, the power transmitter 100transmits a network subscription approval message in step 555 and thenperforming power transmission to the target of charging in step 560.

Meanwhile, as described above, FIGS. 6A and 6B illustrate an example ofa power change according to whether the network subscription requestmessage is received when it is determined that there is the target ofcharging in a state where there is no transmitted power, that is, thecurrent transmission power (P_present) is “0”. The power transmissionfor communication with each power receiver can be controlled even whenthere are a plurality of power receivers in the wireless multi-powertransmission system as shown in FIGS. 7A and 7B. FIGS. 7A and 7B arediagrams illustrating an operation of changing a power transmissionvalue when a target of power reception is additionally detected in astate where there is a power receiver according to an embodiment of thepresent invention.

FIG. 7A illustrates an example where, when the power transmitter 100performs the load measurement 700 in transmitting power having a size ofthe current transmission power (P_present) to the power receiver anddetects that there is a target of charging which can receive power at atime point of E, the power transmitter 100 gradually increases atransmission power value for communication with the target of charging.Similarly to FIG. 7A, FIG. 7B also illustrates an example where, whenthe power transmitter 100 performs the load measurement 710 and detectsthere is a target of charging at a time point of G, the powertransmitter 100 increases a transmission power value for communicationwith the target of charging. However, although the transmission powervalue is increased from the size of the first communication power(P_communicaiton_1) to the size of the third communication power(P_communication_3) in FIG. 7A, the network subscription request messageis not received within the time limit (T_joinlimit) and thus the powertransmitter 100 determines the target of charging as the non-target ofpower reception at a time point of F. Unlike in FIG. 7A, thetransmission power value having the size of the second communicationpower (P_communication_2) is maintained in FIG. 7B when the networksubscription request message is received at a time point of H.

According to embodiments of the present invention as described above, ifthe network subscription request message is not received with the timelimit even though the transmission power value is gradually increasedfor the target of charging which makes the load change, the target ofcharging is determined as the non-target of power reception and thuspower transmission to the target of charging is stopped. If the networksubscription request message is received with the time limit as thetransmission power value is gradually increased, the target of chargingis determined as the normal power receiver and thus the transmissionpower value is maintained.

As described above, through the transmission of the changed transmissionpower value, sufficient power transmission required for operating thepower receiver normally can be achieved.

The power transmitting method for communication with the power receiverin the wireless multi-power transmission system according to embodimentsof the present invention has an advantage of supplying sufficient powerto the power receiver. Further, when the power receiver does not receivesufficient power to communication with the power transmitter, thesufficient power is supplied to the power receiver through additionalpower transmission for the communication by the power transmitter.

Furthermore, even if multiple power receivers are located in theeffective charging area at the same time or one of the multiple powerreceivers is not fully located within the effective charging area,sufficient power can be supplied to each power receiver and thus normalcommunication can be achieved.

While the invention has been shown and described with reference tocertain embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method of controlling power transmission of awireless power transmitter, the method comprising: transmitting, by aresonance signal generator, first power for detecting a change of load;transmitting, by the resonance signal generator, second power having afirst magnitude for communicating with a wireless power receiver, if thechange of load is detected; increasing a magnitude the second power to asecond magnitude which is greater than the first magnitude; receiving,by a wireless communication unit, a network subscription request messagefrom the wireless power receiver, while transmitting the second power;transmitting, by the wireless communication unit, an approval message tothe wireless power receiver; and transmitting, by the resonance signalgenerator, third power to the wireless power receiver, wherein the thirdpower is used for charging in the wireless power receiver.
 2. The methodas claimed in claim 1, further comprising: stopping transmission of thesecond power to the wireless power receiver if the network subscriptionrequest message is not received within a predetermined time through thewireless communication unit.
 3. The method as claimed in claim 1,further comprising: determining whether the wireless power receiver iscapable of subscribing to a wireless multi-power transmission networkusing information in the network subscription request message; andallowing the wireless power receiver to subscribe to the wirelessmulti-power transmission network if the wireless power receiver isdetermined to be capable of subscribing to the wireless multi-powertransmission network.
 4. The method as claimed in claim 3, furthercomprising: denying subscription to the wireless power receiver to thewireless multi-power transmission network if the wireless power receiveris not determined to be capable of subscribing to the wirelessmulti-power transmission network.
 5. The method as claimed in claim 4,further comprising: stopping transmission of the second power to thewireless power receiver after the wireless power receiver is deniedsubscription to the wireless multi-power transmission network.
 6. Themethod as claimed in claim 1, wherein the network subscription requestmessage comprises a protocol version of the wireless power receiver. 7.The method as claimed in claim 1, further comprising: comparing ameasurement value corresponding to the changes of the load with apredetermined threshold value; and detecting the changes of the load ifthe measurement value is greater than or equal to the predeterminedthreshold value.
 8. A wireless power transmitter for controlling powertransmission comprising: a resonance signal generator configured totransmit first power for detecting a change of load; and a wirelesscommunication unit configured to perform wireless communication, whereinthe resonance signal generator is further configured to transmit secondpower having a first magnitude for communicating with a wireless powerreceiver, if the change of load is detected, and increase a magnitude ofthe second power to a second magnitude which is greater than the firstmagnitude; and wherein the wireless communication unit is furtherconfigured to receive a network subscription request message from thewireless power receiver, while the resonance signal generator transmitsthe second power and transmit an approval message to the wireless powerreceiver; wherein the resonance signal generator is further configuredto transmit third power to the wireless power receiver, wherein thethird power is used for charging in the wireless power receiver.
 9. Thewireless power transmitter claimed in claim 8, wherein the resonancesignal generator is further configured to stop transmission of thesecond power to the wireless power receiver if the network subscriptionrequest message is not received within a predetermined time through thewireless communication unit.
 10. The wireless power transmitter claimedin claim 8, wherein the controller determines whether the wireless powerreceiver is capable of subscribing to a wireless multi-powertransmission network using information in the network subscriptionrequest message and allows the wireless power receiver to subscribe tothe wireless multi-power transmission network if the wireless powerreceiver is determined to be capable of subscribing to the wirelessmulti-power transmission network.
 11. The wireless power transmitterclaimed in claim 10, wherein the controller denies subscription to thewireless power receiver to the wireless multi-power transmission networkif the wireless power receiver is not determined to be capable ofsubscribing to the wireless multi-power transmission network.
 12. Thewireless power transmitter claimed in claim 11, wherein the resonancesignal generator is further configured to stop transmission of thesecond power to the wireless power receiver after the wireless powerreceiver is denied subscription to the wireless multi-power transmissionnetwork.
 13. The wireless power transmitter claimed in claim 8, whereinthe network subscription request message comprises a protocol version ofthe wireless power receiver.
 14. The wireless power transmitter claimedin claim 8, wherein the controller compares a measurement valuecorresponding to the changes of the load with a predetermined thresholdvalue and detects the changes of the load if the measurement value isgreater than or equal to the predetermined threshold value.